The present disclosure relates to time-of-flight (TOF) distance measuring systems.
Techniques of measuring a distance to an object are roughly divided into two types. A first-type technique, which may also be called a direct technique, is performed using a ruler, measuring tape, etc. Although the accuracy of the scale of a ruler, etc., directly determines the accuracy of distance measurement, the ruler needs to reach an object. A second-type technique, which may also be called an indirect technique, is commonly performed using trigonometry. This is significantly different from the direct technique in that distance measurement can be achieved without touching an object. The technique utilizing a laser pattern illumination and an image sensor, which has in recent years been applied to game devices, and the 3D imaging technique utilizing two cameras, are considered to be a kind of trigonometric indirect technique.
Time-of-flight (TOF) is another technique of measuring a distance to an object. Specifically, acoustic wave or light is emitted toward an object, a phase difference between a reflected signal and a sound source or light source is detected using a sensor that operates in synchronization with the sound source or light source, and a distance to the object is calculated from the phase difference based on the speed of acoustic wave or light. The TOF technique is considered to be the first type technique, i.e., a kind of direct technique, and also has the advantage of the indirect technique that a distance to a distant object can be measured without physically touching the object.
Japanese Unexamined Patent Publication No. 2007-121116 describes a TOF distance measuring technique using a light source and an image sensor in combination. A TOF distance measuring system employing light includes a light source and a sensor that operates in synchronization with the light source.